Postprandial lipemia is believed to produce a pro-atherogenic state. The magnitude of postprandial lipemia is predictive of risk of atherosclerosis, but the mechanisms responsible for this association are unknown. We hypothesize that fat ingestion induces pro-atherogenic qualitative changes in plasma LDL particles (small and dense, more oxidizable). This hypothesis will be tested in a group of 20 men and women with moderate hyperlipidemia.